The present invention relates to a cylindrical battery wherein discharge performance and reliability are enhanced by improving the mounting structure of the separator that separates the positive electrode material and negative electrode material within the battery, and a method and device for manufacturing such a cylindrical battery.
FIG. 9 is a partially sectioned front view showing a prior art construction of an alkaline dry battery 30 as one example of a cylindrical battery. A battery casing 1 of cylindrical shape having a bottom is integrally provided with a positive electrode projection 6 constituting the positive electrode terminal of the battery, in the middle of its bottom face. This battery casing 1 accommodates positive electrode mixture pellets 2 and a negative electrode gel 4 in the interior thereof, with a tubular separator 35 interposed therebetween. The open end of battery casing 1 is sealed by a sealing plate 7 made of resin, a negative electrode terminal 8 connected to a negative electrode current collector 9 being mounted on this sealing plate 7. Tubular separator 35 is formed in cylindrical shape by winding separator paper into a rolls a portion at the bottom end thereof being folded inwards contacting the bottom face of the battery casing 1 and constituting a bottom part 35a. Since the middle portion of this bottom part 35a is open, a circular bottom separator 36 having a larger diameter than the internal diameter of tubular separator 35 is inserted within tubular separator 35 in order to cover this aperture portion and thereby prevent internal short circuits between negative electrode gel 4 and battery casing 1. Furthermore, a step 1a is provided in the bottom face of battery casing 1, to absorb even if only to a small extent, the thickness of the bottom part 35a of tubular separator 35 and bottom separator 36, so as to avoid, as far as possible, offset in the vertical direction of the reaction surfaces where the negative electrode gel 4 and positive electrode mixture pellets 2 face each other.
The mounting of tubular separator 35 and bottom separator 36 in the manufacturing step of this alkaline dry battery 30 is performed by a manufacturing device shown in FIGS. 10A-10D.
In FIG. 10A, a battery feed jig 15 holding a battery casing 1 is moved directly below a winding rod 33 of a tubular separator installation device 32, after positive electrode mixture pellets 2 have been accommodated in battery casing 1 in a previous step, not shown. The diameter of winding rod 33 below step 38 is formed smaller than the diameter thereabove by an amount corresponding to the thickness of tubular separator 35, and this winding rod is supported such as to be rotated in the forwards and reverse directions and can be raised and lowered. When separator paper, that has been cut to prescribed dimensions, is supplied to the gap between winding rod 33 and winding guides 34, winding rod 33 is rotated in the forwards direction, and the separator paper is wound about the portion of winding rod 33 lower than step 38. In this process, slackness in winding is avoided by pressing the separator paper on to winding rod 33 by means of winding rollers 37. In this way, a tubular separator 35 is formed on winding rod 33 as shown, by winding the separator paper about winding rod 33 a prescribed number of times.
Next, as shown in FIG. 10B, winding rollers 37 are retracted from winding rod 33, winding rod 33 is lowered, and battery feed jig 15 is raised, so that winding rod 33 with tubular separator 35 wound thereon is inserted into battery casing 1. At this point the tubular separator 35, when inserted into battery casing 1, is released from the restraint applied by winding guides 34, so it increases its winding radius by springing back of its own accord so that it is in tight contact with positive electrode mixture pellets 2. Since the tip of tubular separator 35 is wound in a hollow condition with no winding rod 33 at its center, tubular separator 35 is pressed by step 38 and thereby inserted into battery casing 1; furthermore, when it is pressed against the bottom face of battery casing 1, this tip is squeezed inwards. Then, by further pressure applied by the tip of winding rod 33, the bending produced by this squeezing is molded into a flat condition, forming bottom part 35a (see FIG. 9). After this, winding rod 33 is released from tubular separator 35 by backwards rotation and raised, while battery feed jig 15 is lowered, so that tubular separator 35 is left in a condition in which it is installed in battery casing 1.
Battery casing 1 with tubular separator 35 installed therein is then fed to the next step by battery feed jig 15 and, as shown in FIG. 10C, is moved below bottom separator installation device 39. Bottom separator installation device 39 is provided with an insertion rod 40 and insertion guide hole 41; when bottom separator 36 that has been cut to circular shape is supplied to above insertion guide hole 41, insertion rod 40 is lowered. Simultaneously, battery feed jig 15 is raised and the open end of battery casing 1 is brought into contact with a locating element 42 of bottom separator installation device 39. Since insertion guide hole 41 is formed of cylindrical shape of smaller diameter than the diameter of bottom separator 36, when bottom separator 36 is inserted into insertion guide hole 41 by insertion rod 40, the circumferential region of bottom separator 36 is raised, forming a flat-bottomed U-shape in cross-section. When insertion rod 40 is further lowered, as shown in FIG. 10D, bottom separator 36 is installed on bottom part 35a produced by squeezing in of the bottom end of tubular separator 35.
After undergoing the steps of insertion of tubular separator 35 and bottom separator 36, battery casing 1 is fed to the subsequent steps (not shown) to complete the alkaline dry battery 30.
However, the battery construction and its manufacturing steps in the prior art described above were subject to the following problems.
(1) The bottom end part of tubular separator 35 was squeezed inwards to form bottom part 35a and further, in order to block the aperture produced in the middle of bottom part 35a, this aperture portion was closed by placing on bottom part 35a a bottom separator 36. Because of this, since a double-layer structure is adopted in which, in addition to the folding-over produced by squeezing of the bottom part 35a, bottom separator 36 is overlaid thereon, the thickness of the separator portion is increased, resulting in the production of a step (offset in the axial direction) in the reaction surfaces of negative electrode gel 4 and positive electrode mixture pellets 2 that face each other through tubular separator 35. Even though, as described above, a step 1a is provided in the bottom face of battery casing 1, this is still insufficient to eliminate the step previously referred to. Furthermore, the discharge performance of the battery is lowered due to the diminution in capacity to receive the negative electrode gel.
(2) In addition to the overlapping in pleated form of the bottom part 35a produced by the squeezing of the bottom end part of tubular separator 35, due to the double-layer construction with bottom separator 36, a construction is produced in which the separator portion at the bottom of battery casing 1 is resistant to deformation. As a result, if the negative electrode gel 4 is caused to expand by over-discharging, since this expansion force cannot escape at the bottom, the internal pressure produced by the expansion acts on the sealing plate 7, risking failure of the thin part 7a provided in sealing plate 7 The purpose of the provision of this thin part 7a is, in the first place, to prevent bursting of the battery if the internal pressure rises abnormally due to mis-use such as mixing new and old batteries or inserting the wrong way round, and its failure due to expansion of negative electrode gel 4 produced by over-discharging must be avoided.
(3) Since bottom separator 36 is arranged in contact with negative electrode gel 4, which is liable to flow, it can easily be displaced by flow of negative electrode gel 4 if the battery is subjected to shock or vibration. Internal short-circuiting due to displacement of bottom separator 36 can therefore easily occur.
(4) In the step of inserting bottom separators 36 into battery casings 1 by means of bottom separator installation device 39, bottom separators 36 pre-cut to prescribed dimensions and arranged in a stack are supplied by being picked up, one at a time, by vacuum suction. With this method, thin bottom separators 36 cannot be employed, but, when the thickness of bottom separator 36 is large, discharge performance is adversely affected, as described in paragraph (1) above.
(5) Since tubular separator 35 and bottom separator 36 are installed in battery casing 1 in separate steps, the number of steps is increased and productivity lowered, and the size of the manufacturing equipment becomes large.
The present invention has been devised in order to solve the aforementioned problems of the prior art, its object being to provide a method of manufacturing and device therefor whereby a cylindrical battery of high battery performance and reliability can be manufactured in an efficient manner.
A cylindrical battery according to the present invention comprises: a battery casing formed in a cylindrical shape having a bottom and having a projection protruding outwards in the middle of the bottom face; positive electrode mixture pellets formed in cylindrical shape and accommodated in said battery casing; a tubular separator formed in cylindrical shape; negative electrode gel accommodated on an inner side of the positive electrode mixture pellets with said tubular separator interposed therebetween; a bottom separator arranged at the bottom face on the inside of said battery casing; and a sealing plate that seals the open end of said battery casing; wherein said bottom separator is formed in the form of a sheet of thickness less than that of said tubular separator and of dimensions larger than the diameter of tubular separator, being arranged such that a peripheral part thereof is raised at the outside of tubular separator, thereby isolating said negative electrode gel and the battery casing.
With a construction as described above, the capacity to receive the negative electrode gel is increased since the tubular separator is formed without squeezing-in in the inwards direction at its bottom end, and the bottom part of the negative electrode gel and the inner bottom face of the battery casing are separated merely by a thin bottom separator; also, the discharge performance of the battery is improved since the reaction area where the positive electrode mixture pellets and negative electrode gel face each other is increased. Also, since the thin bottom separator is easily deformed and a space formed by a recess in the bottom face of the battery casing is provided at the under-surface of the bottom separator, if the negative electrode gel swells up due to over-discharging etc., this expansion can be absorbed by deformation of the bottom separator towards the space of this recess. Consequently, liquid leakage from the internal pressure release port formed in the sealing plate caused by rise of internal pressure produced by swelling-up of the negative electrode gel can be prevented. Also, since the bottom end of the tubular separator is surrounded from the outside by the peripheral raised portion of the bottom separator, being in a condition sandwiched between the tubular separator and the positive electrode mixture pellets, even if large impacts or vibration are applied to the battery, there is no possibility of the bottom separator being shifted out of position, so leakage of negative electrode gel caused by displacement of the bottom separator from its position can be prevented and there is thus no possibility of internal short circuits arising.
With a cylindrical battery according to the present invention, the bottom separator that isolates the negative electrode gel and battery casing consists of a thin sheet of thickness 0.03 to 0.2 mm; thus, compared with the thick separator of double-layer construction used in the prior art the accommodation capacity for the negative electrode gel is increased and the reaction area is also increased. Also, due to this thinness, the bottom separator can easily be deformed, so if the negative electrode gel swells up on over-discharging, it can deform towards the space constituted by the recess formed at the bottom face of the battery casing, thereby absorbing this expansion. If the thickness of the bottom separator is less than 0.03 mm, it is difficult to construct a uniform thin film and strength is lowered. On the other hand, if the thickness is greater than 0.2 mm, the effect of absorbing expansion by deformation is lowered, so a thickness within this range is appropriate.
Also, since the bottom separator in a cylindrical battery according to the present invention is formed using an ion-permeable sheet, even though its peripheral raised portion is interposed between the positive electrode mixture pellets and negative electrode gel, the reaction of these two is not impeded.
Also, since the bottom separator in a cylindrical battery according to the present invention is formed in rectangular shape, the loss involved in cutting it out from the paper stock can be eliminated and since no cutting-out waste is therefore produced, the time required to dispose of such waste can be eliminated.
In a method of manufacturing a cylindrical battery that is manufactured by inserting positive electrode mixture pellets formed in cylindrical shape into a cylindrical casing having a bottom, inserting a tubular separator so as to contact the inner circumferential surface of said positive electrode mixture pellets, inserting a bottom separator at the bottom face of battery casing, injecting a negative electrode gel into the central space enclosed by the two separators and, and sealing the open end of the battery casing by means of a sealing plate; according to the invention, said bottom separator is formed in the form of a sheet of dimensions larger than the diameter of the tubular separator and both separators are inserted simultaneously into the battery casing with the leading end of the tubular separator in contact with this bottom separator, thereby inserting both separators into the battery casing with the peripheral portion of the bottom separator raised so that the leading end of the tubular separator is surrounded from the outside by the raised portion at the periphery of said bottom separator.
With the method of manufacture described above, the tubular separator and bottom separator can be simultaneously inserted into the battery casing, so the steps of inserting both separators can be combined into one, enabling production efficiency to be raised. Also, since the bottom separator is inserted into the battery casing with the leading end of the tubular separator surrounded from outside by the peripheral raised portion of the bottom separator, even if the battery is subjected to impacts or vibration, the bottom separator cannot easily be displaced from its position. Furthermore, since the portion of the negative electrode gel nearest the bottom face is separated from the battery casing only by the bottom separator, the capacity for negative electrode gel is increased and no step is produced in the reaction face with the positive electrode mixture pellets, so discharge performance can be improved.
Also, in a device for manufacturing a cylindrical battery according to the present invention whereby a cylindrical battery is manufactured by inserting positive electrode mixture pellets formed into cylindrical shape into a cylindrical battery casing having a bottom, then inserting a tubular separator so as to contact the inside circumferential face of said positive electrode mixture pellets and inserting a bottom separator on to the bottom face of battery casing, and injecting a negative electrode gel into the central space enclosed by the separators, comprising: a separator insertion jig including a circular guide hole along whose central axis a tubular separator is passed, a cylindrical part which is below this guide hole and that can be inserted into the open end of battery casing, and a holding part that is above said guide hole, for holding the bottom separator; bottom separator supply means whereby a bottom separator cut to dimensions larger than the diameter of the tubular separator is supplied into the holding part of said separator insertion jig; and separator installation means having a winding rod and whereby a tubular separator is formed by winding separator paper on to this winding rod, and whereby this tubular separator is inserted into the battery casing through said guide hole together with the bottom separator held within the holding part of said separator insertion jig; the separator insertion jig to which the bottom separator has been supplied from said bottom separator supply means, the winding rod of the separator installation means on which a tubular separator has been formed, and the battery casing into which the positive electrode mixture pellets have been inserted are positionally located such that their respective central axes coincide with an identical line; the cylindrical part of the separator insertion jig is fitted onto the open end of the battery casing; and said separator insertion jig, winding rod, and battery casing are relatively moved such that the winding rod is inserted into the battery casing through said guide hole and is then once more returned to said positionally located condition, whereby the tubular separator and the bottom separator are simultaneously installed in the battery casing.
With the manufacturing device described above, the separator installation means holding a tubular separator which has been wound on to a winding rod, and the battery casing are respectively located in position above and below the separator insertion jig, which has a holding part, guide hole, and cylindrical part, and the open end of the battery casing is fitted on to the cylindrical part of the separator insertion jig; the winding rod of the separator installation means is then advanced into the battery casing through the holding part and guide hole of the separator insertion jig. Since the bottom separator is supplied beforehand into the holding part and the tubular separator on the winding rod pushes the bottom separator into the guide hole by means of its tip, the peripheral portion of the bottom separator is raised up and assumes a condition surrounding the tip of the tubular separator and, in this condition, both separators are simultaneously inserted into the battery casing. Since the tubular separator wound on to the winding rod is inserted into the battery casing from the guide hole of the separator insertion jig through its cylindrical part, its wound-up condition is not released until it is inserted into the battery casing i.e. the wound-up condition is only released, by its own spring-back effect, once it has been inserted into the battery casing. It then adheres tightly to the previously inserted positive electrode mixture pellets and is released from the winding rod. At this point the tubular separator can easily be released by rotating the winding rod in the opposite direction to the winding direction. Installation of the two separators is thus simultaneously completed by raising the winding rod from which the tubular separator has been released and lowering the battery casing so that it is released from the cylindrical part of the separator insertion jig.
Since the bottom separator supply means in the manufacturing device described above transfers the bottom separator to the separator insertion jig holding it by vacuum suction immediately after this bottom separator has been cut off from the paper stock, it is possible to effect feed of bottom separators one at a time in a manner linked to the operation of the separator installation step. With the conventional method, in which bottom separators are cut out beforehand and kept in readiness, the small, light and thin bottom separators are difficult to handle and it is difficult to achieve reliable vacuum suction of one separator at a time from the stack of separators. However, with the present invention, by providing the bottom separator cutting-out device in the bottom separator supply means, the step of processing a small part which is difficult to handle can be eliminated.
Furthermore, the bottom separators in the manufacturing device described above are cut out into square shape from the paper stock, so they may be cut from tape-shaped paper stock of width equal to the length of one side of the square shape; in this way, cutting waste is not produced and loss of material is eliminated. Also, the cutting-out device itself can be constructed in a straightforward manner.
Furthermore, as the holding part of the separator insertion jig in the manufacturing device described above comprises an accommodating space formed in circular shape having an internal diameter about the same as the diagonal length of the square-shaped bottom separators, and an insertion hole having a diameter smaller than the diagonal length of the bottom separators and opening at the top of this accommodating space, when a square bottom separator is inserted into the accommodating space from the insertion hole, although the corner parts of the square shape are deformed, since the internal diameter of the circular accommodating space is formed approximately equal to the diagonal length of the square shape, when the bottom separator is inserted into the accommodating space, it returns to a flat condition, being automatically located in position such that the corner parts contact the inner circumferential surface of the accommodating space. Also, holding and positional location of a small, light and thin bottom separator can easily be achieved without its position being displaced by the effects of air currents and/or vibrations produced by movement of the separator insertion jig.